In the operation of certain kinds of apparatus, such as that used in fire-fighting, it is common practice to mix a secondary fluid (such as foam) with a primary fluid (such as water). In many applications, it is important that the exact amount of foam be added to the water for two reasons: first of all, the foam/water combination is most effective when an exact proportion is used. Secondly, using too much foam is a wasteful procedure, since the foam is quite expensive. This problem is exacerbated in the case of a plurality of fire-fighting nozzles, because of the difficulty of selecting the certain amount of foam necessary for each of the nozzles. The secondary fluid or foam is usually added to the water by use of an eductor consisting of a venturi through which water flows. The foam is introduced at the neck of the venturi and is sucked into the main flow in accordance with the induction principle. An eductor works best with a fixed amount of main primary fluid flow. It is difficult to put the eductor in the main stream of water flowing through the pump, because nozzles are being opened and closed in the system as the fire-fighting takes place. For that reason, it is common practice to have a branch circuit flowing from the outlet of the pump to the inlet of the pump and to place the eductor in that branch circuit which contains a small amount of recirculated primary fluid. In order to control the amount of foam that is introduced into the eductor, a variable resistence passage has in the past been inserted between the foam tank and the eductor. When the fire-fighting nozzles are being used, one of the firemen must stand at this device and continuously reset the passage opening to an amount commensurate with the demand on foam by the nozzles then in use. Since the nozzles are cut in and out during the fire-fighting operation, it is necessary for him to reset the resistence passage in accordance with a chart which is mounted on the device. This represents a rather complex situation, since it requires that one of the fire-fighting personnel be devoted entirely to this function. Furthermore, it is difficult for him to reset accurately, particularly if the nozzles are being shut on and off (or having their flow rates changed) at a rapid rate, as is sometimes the case in the case of a fire. One situation in which this problem arises is in the case of a crash truck used at an airport which has a larger number of nozzles in various parts of the truck for performing different functions in fighting an airplane fire. In other words, even if the services of a fireman is devoted solely to the function of regulating the amount of foam introduced into the flow of primary fluid, he is still not able to do so accurately. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a proportioning system for use in fire-fighting equipment, which system automatically regulates the introduction of secondary fluid into a primary fluid flow.
Another object of this invention is the provision of a proportioning system consisting of a plurality of flow regulating passages, each passage being sized for a particular piece of fire-fighting equipment.
A further object of the present invention is the provision of a proportioning system, including a plurality of fire-fighting nozzles and including means for introducing foam into a primary fluid without human supervision in the exact amount necessary at any given moment, depending on the number of nozzles in use.
It is another object of the instant invention to provide a fire-fighting system with automatic regulation of the introduction of foam, which system is inexpensive to manufacture, which is simple in construction, and which is capable of a long life of useful service with a minimum of maintenance.